The sliding cam valve trains, which are known in various configurations, serve for actuating, with variable lift, the gas exchange valves of internal combustion engines. The variability in lift is generated by the camshaft, which includes a carrier shaft and a sliding cam situated thereon rotatably fixed and movable between axial positions. The sliding cam has at least one set of cams, including cams having different bumps, and a groove-like displacement slot into which an actuator pin, which extends out of an actuator, dips in order to move the sliding cam on the carrier shaft between the axial positions and thus to shift the present lift pick-up from one cam to the other cam.
Valve trains including electromagnetic actuators and displacement slots of the type mentioned at the outset are known from DE 10 2007 010 149 A1 with two Y-shaped and circumferentially parallel grooves, from DE 10 2009 053 116 A1 with two X-shaped and circumferentially parallel grooves, and from DE 10 2009 009 080 A1 with two S-shaped grooves arranged circumferentially in series.
The sliding cam switchover process is intended to be able to take place in a precise and reproducible manner even at a preferably high rotational speed of the camshaft and therefore within an extremely short period of time and is intended to be completed for all cylinders of the internal combustion engine within one working cycle and without any shifting errors. Ideally, therefore, all actuators of the valve train are not only sufficiently fast but also are without appreciable time variations with regard to the release and movement behavior of the actuator pins extending out of the actuator. Actuators which are particularly suitable for this have actuator pins which are held in the retracted state by the holding force of a permanent magnet counter to the force of a spring. The actuator pins are released by briefly energizing an electromagnet, which temporarily neutralizes the effect of the permanent magnet, whereupon the actuator pin extends out of the actuator due to the spring force. The return retracting movement into the actuator is brought about by the groove which slopes upward at the end of the displacement slot onto the cylindrical circumference of the slot section. The operating principle of such an actuator is known from EP 1 421 591 B1.